In order to display information, it is known to use in a watch, either an analog display generally formed of hands associated with one or several graduations, or a digital display formed generally by cells of liquid crystals (LCD).
It is also known to use a printed disc or ring associated with an aperture provided in the dial of the watch in order to indicate the date, the day of the week, the month or indeed the year. In order to enlarge the number indicating the date, it is known to arrange-an enlarging lens at the level of the watch crystal opposite the aperture provided in the dial. In such a case, the distance separating the printed disc or ring and the enlarging lens is generally less than 3 mm. Because of this, the focal length of the lens must be very small in order to enable a substantial enlargement. For example, in order to obtain an enlargement by a factor of 2, the focal length is less than 6 mm. Admitting that the aperture has a radius 1 mm and that the eye is about 15 cm from the watch crystal, the enlarging lens must have a radius of approximately 2 mm corresponding to the radius of the virtual image formed by such enlarging lens in order that the date can be read in its entirety by a watch user.
Additionally, with a lens having a focal length of 6 mm, the edge effects are very substantial and the optical aberrations are enormous to an extent such that an enlarging lens having a radius of a dimension substantially double, that is to say on the order of 4 mm, is necessary in order to read the date correctly and easily which is enormous for a focal length of 6 mm.
The above-mentioned arrangement is very unfavourable as far as concerns the overall dimensions of the enlarging lens and the quality of the image formed by such lens remains relatively mediocre. Consequently, the arrangement described hereinbefore is appropriate only for enlargements substantially less than a factor of two. Thus, this arrangement does not permit a substantial increase in the density of information supported by the display arrangement.
The problem set forth hereinbefore demonstrates that in the case in which information is displayed at the dial level, the possibilities of augmenting such information in a significant manner whilst furnishing an enlarged image of good quality enabling easy reading of such information do not exist for watches having conventional dimensions and particularly for wristwatches.